Flame retardant materials have been increasingly needed because of recent strong demands of ensuring safety of food, clothing and shelter. Under such circumstances, many proposals have been made wherein a general-purpose flammable fiber is combined with a flame retardant fiber having a high flame resistance to form a composite material in order to impart a flame resistance to the flammable fiber while maintaining the properties of the flammable fiber. As a method of preparing such a composite material, for instance, Japanese Patents No. 2,593,985 and No. 2,593,986 propose, when combining a halogen-containing flame retardant fiber and a natural fiber, using an antimony compound as a flame retardant to be incorporated into the halogen-containing flame retardant fiber.
Recently, union fabrics prepared using a general-purpose cellulosic fiber as a warp and a halogen-containing flame retardant fiber incorporated with an antimony compound as a weft are popularly used in interior goods such as curtain and upholstery since it is possible to make the best use of the features of the cellulosic fiber such as natural feel, hygroscopic property and heat resistance. Among others, union fabrics having jacquard, dobby or satin structure prepared using a cellulosic fiber as a warp and a flame retardant halogen-containing fiber incorporated with an antimony compound as a weft are characteristic fabrics that the cellulosic fiber appears in a large quantity on the right face of the fabric.
However, even if the above-mentioned technique is applied to these union fabrics, it is the actual situation that they do not pass the M1 class of the highest flame resistance in NF P 92-503 burning test in France which requires a high level of flame resistance.
That is to say, it is the actual situation that none of known union fabrics made of a cellulosic fiber and a flame retardant halogen-containing fiber pass the M1 class of the NF P 92-503 burning test. The reasons are considered to be that the NF P 92-503 burning test is a very severe burning test such that after previously heating a test fabric with an electric heater for 20 seconds, the fabric is ignited and the afterflame time must be within 5 seconds, and that in case of union fabrics having jacquard, dobby or satin structure, there are portions in a fabric where the cellulosic fiber and the flame retardant halogen-containing fiber are unevenly distributed respectively and these portions show a lower flame resistance against this burning test since the heat source is large.
Explaining in more detail, in this burning test both the right face and the reverse face of a fabric are subjected to the test. An antimony compound called a gas type flame retardant is effective against a flame applied to a face on which a cellulosic fiber unevenly appears much and, on the other hand, a tin flame retardant called a carbonizing type flame retardant is effective against a flame applied to a face on which a flame retarded halogen-containing fiber unevenly appears much. However, there has hitherto not been known a flame retardant or a combination of flame retardants which exhibits a combustion-inhibiting effect for both of the face on which the cellulosic fiber appears much and the face on which the cellulosic fiber appears only slightly.
Thus, it has been desired to develop a union fabric which shows a high flame resistance even in a combination of a flame retarded halogen-containing fiber and a cellulosic fiber and which is classified into the M1 class of the NF P 92-503 burning test in France.
Thus, the present inventors repeatedly made a study on a union fabric comprising a modacrylic fiber as a flame-retarded halogen-containing fiber and a cellulosic fiber. As a result, the present inventors have found that a high flame resistance can be exhibited even with respect to union fabrics such as those having jacquard, dobby or satin structure when a predetermined amount of an antimony compound and a predetermined amount of a zinc stannate compound are used in combination as a flame retardant to be added to the modacrylic fiber, thus having accomplished the present invention.